Reportable Operating Segments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Non-interest revenues	$ 8,934	$ 6,877	$ 24,593	$ 20,648
Revenue from contracts with customers	7,139	5,380	19,555	16,033
Interest income	2,301	2,324	6,633	7,796
Interest expense	307	450	991	1,708
Total revenues net of interest expense	10,928	8,751	30,235	26,736
Pretax segment income (loss)	2,450	1,364	8,383	2,438
Total assets	184,261	187,000	184,261	187,000	$ 191,367
Corporate and Other
Segment Reporting Information [Line Items]
Non-interest revenues	(23)	(79)	(159)	(200)
Revenue from contracts with customers	(7)	(6)	(20)	(22)
Interest income	40	53	126	232
Interest expense	46	86	178	432
Total revenues net of interest expense	(29)	(112)	(211)	(400)
Pretax segment income (loss)	(285)	(359)	(805)	(1,097)
Total assets	30,000	53,000	30,000	53,000
GCSG | Operating Segments
Segment Reporting Information [Line Items]
Non-interest revenues	4,699	3,632	12,982	10,662
Revenue from contracts with customers	3,392	2,476	9,229	7,205
Interest income	1,879	1,916	5,436	6,298
Interest expense	174	244	536	844
Total revenues net of interest expense	6,404	5,304	17,882	16,116
Pretax segment income (loss)	1,488	1,125	5,525	2,227
Total assets	92,000	82,000	92,000	82,000
GCS | Operating Segments
Segment Reporting Information [Line Items]
Non-interest revenues	2,978	2,327	8,225	7,129
Revenue from contracts with customers	2,556	1,969	7,019	5,993
Interest income	378	351	1,059	1,252
Interest expense	111	139	338	493
Total revenues net of interest expense	3,245	2,539	8,946	7,888
Pretax segment income (loss)	718	272	2,222	269
Total assets	48,000	40,000	48,000	40,000
GMNS | Operating Segments
Segment Reporting Information [Line Items]
Non-interest revenues	1,280	997	3,545	3,057
Revenue from contracts with customers	1,198	941	3,327	2,857
Interest income	4	4	12	14
Interest expense	(24)	(19)	(61)	(61)
Total revenues net of interest expense	1,308	1,020	3,618	3,132
Pretax segment income (loss)	529	326	1,441	1,039
Total assets	$ 14,000	$ 12,000	$ 14,000	$ 12,000